Tessaiga (“S?Ó‰å, also known as Tetsusaiga) is a fictional sword in the anime and manga series "Inuyasha," wielded by a half-human, half-demon (”¼—d, or hanyou) of the same name. The kanji, directly translated, means "iron-crushing fang."

In the English adaptations of Inuyasha, Tessaiga is written Tetsusaiga (or Tetsaiga) due to an error in translation in the early days of the manga when the tiny ‚Á (tsu) kana (which indicates a glottal stop, or a doubling of the consonant that follows it) was misread as a full-sized ‚Â (tsu) kana, altering the romanization and pronunciation of the word. Both Tetsusaiga and Tessaiga can come from the kanji; the proper spelling depends on how the name is pronounced. The proper romanization, however, is Tessaiga. By the time Viz, the company that translates the anime and manga, had realized the error it was too late.
I'm going to beat you down with (my) Tessaiga!
by Rubyhatchet May 5, 2005